Exhaust flow modifier, duct intersection incorporating the same, and methods therefor

ABSTRACT

A duct intersection comprising a first duct portion and a second duct portion extending laterally from a side of the first duct portion. At least one flow modifier is mounted inside one of the first and second duct portions. The flow modifier is a contoured duct liner and/or the flow modifier includes at least one turning vane. The duct intersection may also include a transition portion extending between the first and second duct portions, wherein the transition portion has a length extending along a side of the first duct portion and a depth extending away from the side of the first duct portion, wherein the length is greater than a diameter of the second duct portion.

TECHNICAL FIELD

The present technology is generally directed to devices and methods formodifying fluid flow within a duct. More specifically, some embodimentsare directed to flow modifiers and transition portions for improving theexhaust flow from a coke oven through a duct intersection.

BACKGROUND

Coke is a solid carbonaceous fuel that is derived from coal. Because ofits relatively few impurities, coke is a favored energy source in avariety of useful applications. For example, coke is often used to smeltiron ores during the steelmaking process. As a further example, coke mayalso be used to heat commercial buildings or power industrial boilers.

In a typical coke making process, an amount of coal is baked in a cokeoven at temperatures that typically exceed 2000 degrees Fahrenheit. Thebaking process transforms the relatively impure coal into coke, whichcontains relatively few impurities. At the end of the baking process,the coke typically emerges from the coke oven as a substantially intactpiece. The coke typically is removed from the coke oven, loaded into oneor more train cars (e.g., a hot car, a quench car, or a combined hotcar/quench car), and transported to a quench tower in order to cool or“quench” the coke before it is made available for distribution for useas a fuel source.

The hot exhaust (i.e. flue gas) is extracted from the coke ovens througha network of ducts, intersections, and transitions. The intersections inthe flue gas flow path of a coke plant can lead to significant pressuredrop losses, poor flow zones (e.g. dead, stagnant, recirculation,separation, etc.), and poor mixing of air and volatile matter. The highpressure drop losses lead to higher required draft which can lead toleaks and a more difficult to control system. In addition, poor mixingand resulting localized hot spots can lead to earlier structuraldegradation due to accelerated localized erosion and thermal wear.Erosion includes deterioration due to high velocity flow eating away atmaterial. Hot spots can lead to thermal degradation of material, whichcan eventually cause thermal/structural failure. This localized erosionand/or hot spots can, in turn, lead to failures at duct intersections.For example, the intersection of a coke plant's vent stack and crossoverduct is susceptible to poor mixing/flow distribution that can lead tohot spots resulting in tunnel failures.

Traditional duct intersection designs also result in significantpressure drop losses which may limit the number of coke ovens connectedtogether in a single battery. There are limitations on how much draft acoke plant draft fan can pull. Pressure drops in duct intersections takeaway from the amount of draft available to exhaust flue gases from thecoke oven battery.

These and other related problems with traditional duct intersectiondesign result in additional capital expenses. Therefore, a need existsto provide improved duct intersection/transitions that can improvemixing, flow distribution, minimize poor flow zones (e.g. dead,stagnant, recirculation, separation, etc.), and reduce pressure droplosses at the intersection thereby leading to improved coke plantoperation as well as potentially lower costs to design, build, andoperate a coke plant.

SUMMARY

Provided herein are contoured duct liners, turning vanes, transitionportions, duct intersections, and methods of improving gas flow in anexhaust system. In an exemplary embodiment, a duct intersectioncomprises a first duct portion and a second duct portion extendinglaterally from a side of the first duct portion. The second duct portionmay tee into the first duct portion. The second duct portion may extendlaterally from the side of the first duct portion at an angle of lessthan 90 degrees.

At least one flow modifier is mounted inside one of the first and secondduct portions. In one aspect of the technology described herein, theflow modifier is a contoured duct liner. In another aspect of thepresent technology, the flow modifier includes at least one turningvane.

In an embodiment, the contoured duct liner comprises a first contouredwall mated to an inside surface of the duct and a second contoured wallmated to the first contoured wall. In one aspect of the presenttechnology, the contoured duct liner may be mounted inside the firstduct portion. In another aspect of the present technology, the contouredduct liner is mounted inside the second duct portion. The secondcontoured wall may comprise a refractory material.

In another embodiment, the contoured duct liner comprises a first wallcontoured to mate with an inside surface of a duct intersection and asecond wall attached to the first wall. The second wall is contoured tomodify the direction of gas flow within the duct intersection. In oneaspect of the present technology, the second wall includes at least oneconvex surface.

In yet another embodiment, the duct intersection comprises a first ductportion and a second duct portion extending laterally from a side of thefirst duct portion. A transition portion extends between the first andsecond duct portions, wherein the transition portion has a lengthextending along a side of the first duct portion and a depth extendingaway from the side of the first duct portion. In an embodiment, thelength is a function of the diameter of the second duct portion. Inanother embodiment, the length is greater than a diameter of the secondduct portion. In a still further embodiment, the length is twice thedepth.

Also provided herein is a coking facility exhaust system. In anembodiment the exhaust system comprises an emergency stack and acrossover duct extending laterally from a side of the emergency stack.The system also includes a contoured duct liner including a first wallmated to an inside surface of the emergency stack and a second wallattached to the first wall. The second wall is contoured to modify thedirection of gas flow proximate an intersection of the emergency stackand crossover duct. The exhaust system may further comprise a secondcontoured duct liner mated to an inside surface of the crossover duct.

Also contemplated herein are methods for improving gas flow in anexhaust system. In one embodiment the method may include determining alocation of a poor flow zone (e.g. dead, stagnant, recirculation,separation, etc.) within the duct intersection and mounting a flowmodifier in the duct intersection at the determined location. In oneaspect of the disclosed technology, the location is determined with acomputer aided design system, such as a computational fluid dynamics(CFD) system. In other aspects of the disclosed technology, the locationis determined by measuring conditions at the duct intersection, such astemperature, pressure, and/or velocity.

In another embodiment, a method of improving gas flow in an exhaustsystem including at least one duct intersection comprises determining alocation of a poor flow zone within the duct intersection and injectinga fluid into the duct intersection at the determined location.

These and other aspects of the disclosed technology will be apparentafter consideration of the Detailed Description and Figures herein. Itis to be understood, however, that the scope of the invention shall bedetermined by the claims as issued and not by whether given subjectmatter addresses any or all issues noted in the background or includesany features or aspects recited in this summary.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the devices, systems, andmethods, including the preferred embodiment, are described withreference to the following figures, wherein like reference numeralsrefer to like parts throughout the various view unless otherwisespecified.

FIG. 1 is a schematic representation of a coke plant;

FIG. 2 is a schematic representation of a representative coke oven andassociated exhaust system;

FIG. 3 is a side view in cross-section of an emergency stack andcross-over duct intersection indicating various flow anomalies near theintersection;

FIG. 4 is a side view in cross-section of a duct intersection accordingto an exemplary embodiment;

FIG. 5 is a perspective view of a fan manifold that extends between theduct fan and main stack of a coke plant;

FIG. 6 is a side view in cross-section of a traditional fan manifoldindicating the velocity of gases traveling through the manifold and mainstack;

FIG. 7 is a side view in cross-section of a modified fan manifoldindicating the velocity of gases traveling through the manifold and mainstack;

FIG. 8 is a side view in cross-section of a turning vane assemblyaccording to an exemplary embodiment;

FIG. 9 is a perspective view of the turning vane assembly shown in FIG.8;

FIG. 10 is a side view in cross-section of a fan manifold according toan exemplary embodiment indicating the velocity of gases travelingthrough the manifold and main stack;

FIG. 11A is a front view schematic representation of a duct intersectionaccording to an exemplary embodiment;

FIG. 11B is a side view schematic representation of the ductintersection shown in FIG. 11A;

FIG. 12A is a front view schematic representation of a duct intersectionaccording to an exemplary embodiment;

FIG. 12B is a side view schematic representation of the ductintersection shown in FIG. 12A;

FIG. 13 is a side view of a duct intersection according to anotherexemplary embodiment;

FIG. 14 is a schematic representation of a fluid injection system foruse at a duct intersection;

FIG. 15A is a perspective view of an intermediate HRSG tie in withtransition pieces at the tie-in joints;

FIG. 15B is a side view of an intermediate HRSG tie in with transitionpieces at the tie-in joints;

FIG. 15C is a perspective view of an intermediate HRSG tie in withtransition pieces at the tie-in joints; and

FIG. 15D is a top view of an intermediate HRSG tie in with transitionpieces at the tie-in joints.

DETAILED DESCRIPTION

Provided herein is a contoured duct liner, a duct intersection, andmethods of improving gas flow in an exhaust system. The describedembodiments may be implemented as original designs or as retrofits toexisting facilities. The disclosed designs have been found to improveflow, thermal conditions, and structural integrity at intersections ortie-ins in a coke oven or similar system. By optimizing the externaland/or internal shape of intersections, the mixing can be improved,areas of relatively undesirable conditions can be minimized, andpressure drop losses at the intersection can be minimized. Reducingpressure losses at the intersections can help lower draft set point(s),which can lead to improved operation as well as potentially lower costdesigns and maintenance. Furthermore, it can be advantageous to minimizethe draft set point of the overall system to minimize infiltration ofany unwanted outside air into the system.

Specific details of several embodiments of the technology are describedbelow with reference to FIGS. 1-14. Other details describing well-knownstructures and systems often associated with coke making and/or ductdesign have not been set forth in the following disclosure to avoidunnecessarily obscuring the description of the various embodiments ofthe technology. Many of the details, dimensions, angles, and otherfeatures shown in the figures are merely illustrative of particularembodiments of the technology. Accordingly, other embodiments can haveother details, dimensions, angles, and features without departing fromthe spirit or scope of the present technology. A person of ordinaryskill in the art, therefore, will accordingly understand that thetechnology may have other embodiments with additional elements, or thetechnology may have other embodiments without several of the featuresshown and described below with reference to FIGS. 1-14.

FIG. 1 illustrates a representative coke plant 5 where coal 1 is fedinto a battery of coke ovens 10 where the coal is heated to form coke.Exhaust gases (i.e. flue gases) from the coke ovens are collected in acommon tunnel 12 which intersects emergency stack 14. Cross-over duct 16is also connected to common tunnel 12 via the emergency stack 14. Hotflue gases flow through the cross-over duct 16 into a co-generationplant 18 which includes a heat recovery steam generator (HRSG) 20 whichin turn feeds steam turbine 22. The flue gases continue on to a sulfurtreatment facility 24 and finally the treated exhaust gases are expelledthrough main stack 28 via duct fans 26, which provide negative pressureon the entire system in addition to the draft created by gases risingthrough the main stack 28.

With further reference to FIG. 2, it can be appreciated that coke ovens10 are connected to the common tunnel 12 via uptakes 15. Common tunnel12 extends horizontally along the top of the coke ovens 10. An emergencystack 14 extends vertically from common tunnel 12 as shown. Cross-overduct 16 intersects emergency stack 14 at a duct intersection 30. Innormal operation, the emergency stack 14 is closed whereby exhaust gasestravel through the cross-over duct 16 to the co-generation plant 18 (seeFIG. 1). In the event of a problem with the co-generation plant 18, orother downstream equipment, the emergency stack 14 may be opened toallow exhaust gases to exit the system directly. While the figures showthe common tunnel 12 and cross-over duct 16 intersecting the emergencystack 14 at different elevations, the common tunnel 12 and cross-overduct 16 may intersect the emergency stack 14 at the same elevation.Furthermore, the technology disclosed herein may be applied to theintersections whether they are at the same elevation or differentelevations.

FIG. 3 illustrates various flow anomalies present in traditional ductintersections, such as duct intersection 30. Flow anomaly 32 is a pointof localized combustion that is due to poor flow/distribution. Anadditional area of poor flow/mixing distribution 36 is located in theemergency stack 14 across from the cross-over duct 16. A poor flow zone34 (e.g. dead, stagnant, recirculation, separation, etc.) is located incross-over duct 16. These poor flow zone areas contain separated flowswhich can dissipate useful flow energy. These potential poor flow spacescan also contain unwanted, unsteady vortical flow, sometimes enhanced bybuoyancy or chemical reactions, which can contribute to unwanted, pooracoustics, forced harmonics, potential flow instabilities, and incorrectinstrument readings. Incorrect instrument readings may occur ifmeasurements are made in a poor flow zone that has conditions notrepresentative of flow in the duct. Because of the nature of the poorflow zones, these areas can also cause particle drop out and promoteparticle accumulation.

FIG. 4 illustrates an improved duct intersection 130 according to anexemplary embodiment. Duct intersection 130 includes a first ductportion in the form of emergency stack 114 and a second duct portion inthe form of cross-over duct 116 that extends laterally from a side ofthe emergency stack 114. In this embodiment, duct intersection 130includes a plurality of flow modifiers (40, 42, 44) to improve exhaustflow. For example, flow modifier 40 is in the form of a contoured ductliner that is positioned at the intersection 130 of emergency stack 114and cross-over duct 116. Flow modifier 40 occupies the area wheretraditional designs have poor flow and mixing such as flow anomaly 32 inFIG. 3. Flow modifier 42 is disposed in cross-over duct 116 to occupythe poor flow zone 34 shown in FIG. 3. Flow modifier 44 is disposed inthe emergency stack 114 opposite the cross-over duct 116 and, in thiscase, occupies the poor mixing distribution region 36 shown in FIG. 3.With the addition of flow modifiers 40, 42, and 44 the flow F withinintersection 130 is improved (see FIG. 4).

The duct liners reshape the internal contours of the duct, inherentlychanging the nature and direction of the flow path among other effects.The duct liners can be used to smooth or improve flow entrance orprovide better transition from one path to another especially when thereare limitations to do so with the duct shape. The contoured duct linerscan be used to alleviate wall shear stress/erosion stemming from highvelocities and particle accumulation from settling and/or particleimpaction, which could result in slow or poor flow zones. The contouredduct liners also provide better duct transitions, or paths, for betterflow transition and movement, mitigation of stress and thermalconcentrations, and mitigation of flow separation, etc.

With continued reference to FIG. 4 it can be appreciated that, in thisembodiment, the contoured duct liners 40, 42, and 44 are each comprisedof a first contoured wall mated to an inside surface of the ductintersection and a second contoured wall mated to the first contouredwall. For example, contoured duct liner 40 includes a first contouredwall 50 which is mated to the inside surface 17 of emergency stack 114and inside surface 19 of cross-over duct 116. Duct liner 40 alsoincludes a second contoured wall 52 that is mated to the first contouredwall 50. In this case, the second contoured wall 52 is convex andextends into the flow F of the flue gases traveling through the ductintersection 130. Contoured duct liner 42 includes a first contouredwall 54 which is mated to an inside surface 19 of the cross-over duct116. A second contoured wall 56 is mated to the first contoured wall 54and is also convex. Similarly, contoured duct liner 44 includes a firstcontoured wall 58 mated to inside surface 17 of the emergency stack 114and includes a second contoured wall 60 mated to the first contouredwall 58.

The first contoured walls of the contoured duct liners may be attachedto the inside surfaces 17 and 19 by welding, fasteners, or the like.Similarly, the second contoured walls may be attached to theirrespective first contoured walls by appropriate fasteners or by welding.As one of ordinary skill in the art will recognize, the contoured ductliners may be comprised of various materials which are suitable forcorrosive, high heat applications. For example, first contoured walls50, 54, and 58 may be comprised of steel or other suitable material. Thesecond contoured walls 52, 56, and 60 may comprise a refractory materialsuch as ceramic that is capable of resisting the heat associated withthe flue gases and local combustion. The selection of materials can bedependent on the thermal, flow, and chemical properties of the fluegases. Because the flue gases can be of varied temperatures, velocities,chemical composition, in which all can depend on many factors such asthe time in the coking cycle, flow control settings, ambient conditions,at the locations in the coking oven system, etc., the material selectioncan vary as well. The internal lining layers for the hot duct tie-inscould have more significant refractory layers than for cold ducts.Selection of appropriate materials may take into account min/maxtemperatures, thermal cycling, chemical reactions, flow erosion,acoustics, harmonics, resonance, condensation of corrosive chemicals,and accumulation of particles, for example.

In an embodiment, the flow modifiers may comprise a multilayer liningthat is built up with a relatively inexpensive material and covered witha skin. In yet another embodiment, refractory or similar material can beshaped via gunning (i.e. spraying). Better control of shaping viagunning may be accomplished by gunning in small increments or layers. Inaddition, a template or mold may be used to aid the shaping via gunning.A template, mold, or advanced cutting techniques may be used to shapethe refractory (e.g. even in the absence of gunning for the main shapeof an internal insert) for insertion into the duct and then attached viagunning to the inner lining of the duct. In yet another embodiment, theflow modifier may be integrally formed along the duct. In other words,the duct wall may be formed or “dented” to provide a convex surfacealong the interior surface of the duct. As used herein, the term convexdoes not require a continuous smooth surface, although a smooth surfacemay be desirable. For example, the flow modifiers may be in the form ofa multi-faceted protrusion extending into the flow path. Such aprotrusion may be comprised of multiple discontinuous panels and/orsurfaces. Furthermore, the flow modifiers are not limited to convexsurfaces. The contours of the flow modifiers may have other complexsurfaces that may be determined by CFD analysis and testing, and can bedetermined by design considerations such as cost, space, operatingconditions, etc.

FIG. 5 illustrates a traditional fan manifold 70 that extends betweenthe duct fans 26 and main stack 28 (see FIG. 1). Fan manifold 70comprises a plurality of branches 72, 74, and 76 which all intersectinto plenum 80. As shown in the figure, branches 74 and 76 include flowdiverters 78 while plenum 80 includes flow straightener 79. Withreference to FIG. 6, which indicates velocity magnitude in the fanmanifold 70, traditional fan manifold designs result in a high velocityflow 82 which can damage the duct as a result of high shear stress. Incontrast, FIG. 7 illustrates a fan plenum 180 intersection whichincludes a turning vane assembly 90. In this case, the magnitude of thevelocity flowing next to the surface of main stack 128 is much lowerthan in the conventional duct configuration shown in FIG. 6. The higherflow velocity 184 is displaced inward away from the inside wall of themain stack 128, thereby reducing shear stress on the wall and helping toprevent erosion and corrosion of the stack. Turning vanes inside theduct help direct the flow path for a more efficient process. Turningvanes can be used to better mix flow, better directing of flow, andmitigation of total pressure losses, for example.

With reference to FIGS. 8 and 9, the turning vane assembly 90 includesan inner vane 92 and an outer vane 94. In this embodiment, both theinner and outer vanes are disposed in the main stack 128. FIG. 8provides exemplary dimensions by which a turning vane assembly could beconstructed. However, these dimensions are exemplary and otherdimensions and angles may be used. As perhaps best shown in FIG. 9 theinner vane 92 includes a leading portion 902 that connects to an angledportion 904, which, in turn, connects to trailing portion 906. As shownin the figure, the angled portion 904 tapers from a 100 inch width to an80 inch width. Similarly, the trailing portion 906 tapers from an 80inch width to a 50 inch width. Here again, the dimensions are onlyrepresentative and may vary. In this embodiment, the angled portion 904is angled at approximately 45 degrees; however, other angles may be useddepending on the particular application. Outer vane 94 includes aleading portion 908 connected to an angled portion 910 which in turn isconnected to a trailing portion 912. Outer turning vane 94 also includesside walls 914 and 916 as shown. Side walls 914 and 916 are cantedinward towards the angled and trailing portions 910 and 912 at an angleA. In this embodiment angle A is approximately 10 degrees. Turning vaneassembly 90 may be mounted or assembled into the main stack 128 withsuitable fasteners or may be welded in place, for example.

In an exemplary embodiment shown in FIG. 10, a fan manifold plenum 280intersects main stack 228 with a ramped transition. In this case, it canbe appreciated that the fan manifold plenum 280 has an upper wall 281which transitions into the main stack 228 at an angle. As shown by thevelocity magnitude 282, this results in a lower flow velocity magnitudethan with traditional fan manifold designs shown in FIGS. 5 and 6. Ithas been found that improving the intersection/transition from the ductfan to the main stack can reduce wear and erosion as well as ash buildupin the main stack. In addition to the ramped transition, contoured ductliners and/or turning vanes may be used together in combination. Forexample, contoured duct liners may be located in the slower velocityregions 202, 204, and 206 as shown in FIG. 10.

FIGS. 11A and 11B illustrate a duct intersection 230 according toanother exemplary embodiment. In this embodiment, the duct intersection230 includes an emergency stack 214 and a cross-over duct 216 with atransition portion 240 extending therebetween. Changing the size of theduct cross sectional areas near or at intersections can help improveflow performance. In general, increasing the size of the flow crosssectional area as in transition portion 240 can help reduce flow losses.The transition portion can help better transition flow from a duct to ajoining duct at tie-ins or intersections. The transitions can be flared,swaged, swept, or the like to provide the desired flow behavior at theintersections. In addition, the transitions may converge or diverge withrespect to the direction of flow. Converging and diverging portions maybe used in combination, e.g. the duct may first converge and thendiverge or vice versa. Furthermore, it should be understood that theembodiments may be implemented in various combinations. For example, aturning vane assembly, such as described above with respect to FIGS.7-9, may be used in conjunction with the duct liners, whether fabricatedor gunned in place, as well as transition portions.

The transition portion 240 has a length L extending along a side of theexhaust duct and a depth D extending away from the side of the exhaustduct. In this embodiment, the length is greater than a diameter d of thecross-over duct 216. The length L may be a function of the duct diameterd or the depth D. For example, the length L may be twice the depth D.FIGS. 12A and 12B illustrate a duct intersection 330 including atransition portion 340 that is similar to that shown in FIGS. 11A and11B, except in this case the exhaust stack 314 includes an enlargedannular region 315 that is adjacent to the intersection 330. FIG. 13illustrates yet another embodiment of a duct intersection 430 with anasymmetric transition portion 440. Depending on the desired designperformance, external fins could be added to help enhance heat transferwith the surrounding ambient air. For example, external fins from thesurfaces could be used to help cool localized hot spots.

Duct intersections can be designed, retrofitted, or modified tointroduce fluids such as oxidizers (for better combustion or to removePIC's, products of incomplete combustion), liquids such as water, fuels,inert gases, etc. to help better distribute combustion and mitigate hotspots or allow cooling of the hot stream. For example, fluid could beintroduced to provide a boundary layer of cold inert fluid to mitigatehot spots at affected wall surfaces. The fluids, which could includeliquids such as water, inert or other gases, could be used for coolingor mitigating certain chemical reactions. The ducts can be modified toaccommodate ports or additional pathways for introducing fluids. Fluidintroduction, if introduced from a pressurized source, could also createentrainment, thereby improving mixing or flow energy.

FIG. 14 illustrates a duct intersection 530 including a fluid injectionsystem 540. Fluid injection system 540 is operative to inject fluid atparticular regions in the intersection 530 to energize or direct flow,as well as insulate the surface of the ducts from exhaust gases. Fluidinjection system 540 includes a controller 542 which is connected to aplurality of valves, or fluid injectors 544, via wiring 548. Eachinjector 544 is connected by tubing 546 to a fluid reservoir 550. Itshould be understood that the term fluid encompasses liquids as well asgases. Thus, the injection system 540 may inject liquids or gases intothe exhaust flow. The injectors may be spaced optimally depending ondesign conditions. The injectors can inject fluid transversely into theduct, as shown in FIG. 14. Alternatively, the injectors could injectexternal fluid axially or along the exhaust flow direction at variouslocations. The injectors could also inject fluid at different injectionangles. The direction and method of injection depends on the conditionsthat exist at the tie-ins and intersections. The injected fluid may comefrom an external pressurized source. In another embodiment, the fluidmay be entrained through a port or valve by the draft of the exhaustflow.

The fluid injection system 540 may also include various sensors, such astemperature sensor 552 connected to controller 542 via cable 554.Various sensors, such as sensor 552, may provide feedback to controller542 such that fluid may be injected at appropriate times. While theembodiment is illustrated as having a single temperature sensor, otheradditional sensors of different types of sensors may be employed inproviding control feedback to controller 542. For example, other sensormay include pressure, velocity, and emissions sensors, such as an oxygensensor.

The fluid injection system 540 may be used in conjunction with thecontoured duct liners, turning vanes, and transition portions disclosedabove. The contoured duct liners in conjunction with the fluid injectionsystem may extend the use of the duct intersection as a true mixing zoneand potentially a combustion chamber. Air and other additives (e.g.oxygen) may be injected into the intersection to allow better combustionand use of the tunnels as extended combustion zones. Also, a well-mixedduct intersection may be configured to act as a second combustionchamber. The addition of extra air into the duct intersection mixingzone can burn any excess flue gas and even cool off the intersectionwith excess air or other gases, such as nitrogen. For example, if thecommon tunnel is too hot and fully combusted, air may be injected tocool the process. In contrast, if the flue gas is not completelycombusted before entering the heat recovery steam generator (HRSG), itcould reduce the HRSG tubes, which are typically made of metal, leadingto accelerated corrosion and failure. In this case, an oxidizer isadded, such as air, to burn all the combustibles before entering theHRSG.

Although the embodiments have been described with respect to a ductintersection between an emergency stack and cross-over duct, thedisclosed technology may be applicable to hot duct tie-ins, cold ducttie-ins, stack junctions, and HRSGs. For example, as shown in FIGS.15A-15D, an intermediate HRSG tie in may include transition pieces (632,634, 652) at the tie-in joints. Transitions 632 and 634 connect duct 622to duct 630. Duct 630 connects to a rectangular tube 650 via transitionpiece 652.

Also contemplated herein are methods of improving gas flow in an exhaustsystem that includes at least one duct intersection. The methods mayinclude any procedural step inherent in the structures described herein.In an embodiment, the method comprises determining a location of a lowor poor flow zone, an area of poor combustion, or an area of poor mixing(i.e. areas of relatively undesirable conditions) within the ductintersection and providing a flow modifier at the determined location.Providing a flow modifier may include, for example and withoutlimitation, mounting a duct liner within the duct, gunning a refractorymaterial to the inside of the duct, mounting turning vanes within theduct, forming a convex surface along the duct, and combinations of theabove. The location may be determined with a computer aided designsystem, such as a CFD system. The location may also be determined bymeasuring conditions at the duct intersection, such as temperature,pressure, and velocity. In another embodiment the method comprisesdetermining a location of a poor flow zone within the duct intersectionand injecting a fluid into the duct intersection at the determinedlocation.

From the foregoing it will be appreciated that, although specificembodiments of the technology have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the technology. Further, certain aspects of thenew technology described in the context of particular embodiments may becombined or eliminated in other embodiments. Moreover, while advantagesassociated with certain embodiments of the technology have beendescribed in the context of those embodiments, other embodiments mayalso exhibit such advantages, and not all embodiments need necessarilyexhibit such advantages to fall within the scope of the technology.Accordingly, the disclosure and associated technology can encompassother embodiments not expressly shown or described herein. Thus, thedisclosure is not limited except as by the appended claims.

Examples:

-   -   1. A duct intersection, comprising:    -   a first duct portion;    -   a second duct portion extending laterally from a side of the        first duct portion; and    -   at least one flow modifier disposed inside one of the first and        second duct portions.    -   2. The duct intersection according to claim 1, wherein the flow        modifier is a contoured duct liner.    -   3. The duct intersection according to claim 2, wherein the        contoured duct liner comprises a first contoured wall mated to        an inside surface of the duct and a second contoured wall mated        to the first contoured wall.    -   4. The duct intersection according to claim 3, wherein the        second contoured wall comprises a refractory material.    -   5. The duct intersection according to claim 2, wherein the        second duct portion tees into the first duct portion.    -   6. The duct intersection according to claim 5, wherein the        contoured duct liner is mounted inside the first duct portion.    -   7. The duct intersection according to claim 5, wherein the        contoured duct liner is mounted inside the second duct portion.    -   8. The duct intersection according to claim 1, wherein the flow        modifier includes at least one turning vane.    -   9. The duct intersection according to claim 1, wherein the flow        modifier comprises molded refractory material.    -   10. The duct intersection according to claim 1, wherein the        second duct portion extends laterally from the side of the first        duct portion at an angle of less than 90 degrees.    -   11. A contoured duct liner for use in a duct intersection,        comprising:    -   a first wall contoured to mate with an inside surface of a duct        intersection; and    -   a second wall attached to the first wall, wherein the second        wall is contoured to modify the direction of gas flow within the        duct intersection.    -   12. The contoured duct liner according to claim 11, wherein the        second wall includes at least one convex surface.    -   13. The contoured duct liner according to claim 11, wherein the        second wall comprises a refractory material.    -   14. A coking facility exhaust system, comprising:    -   an emergency stack;    -   a crossover duct extending laterally from a side of the        emergency stack; and    -   a contoured duct liner, including a convex surface operative to        modify the direction of gas flow proximate an intersection of        the emergency stack and crossover duct.    -   15. The coking facility exhaust system according to claim 14,        further comprising a second contoured duct liner disposed on an        inside surface of the crossover duct.    -   16. An improved coking facility exhaust system including an        emergency stack and a crossover duct extending laterally from a        side of the emergency stack, the improvement comprising:    -   a contoured duct liner, including a convex surface operative to        modify the direction of gas flow proximate an intersection of        the emergency stack and crossover duct.    -   17. A method of improving gas flow in an exhaust system        including at least one duct intersection, the method comprising:    -   determining a location having undesirable flow characteristics        within the duct intersection; and    -   providing a flow modifier in the duct intersection at the        determined location.    -   18. The method according to claim 17, wherein the location is        determined with a computer aided design system.    -   19. The method according to claim 17, wherein the location is        determined by measuring conditions at the duct intersection.    -   20. The method according to claim 19, wherein the conditions are        selected from the group consisting of temperature, pressure, and        velocity.    -   21. The method according to claim 17, wherein the flow modifier        is a contoured duct liner.    -   22. The method according to claim 17, wherein the flow modifier        is at least one turning vane.    -   23. The method according to claim 17, further comprising gunning        refractory material on an inside surface of the duct        intersection at the determined location, thereby providing the        convex surface.    -   24. A duct intersection, comprising:    -   a first duct portion;    -   a second duct portion extending laterally from a side of the        first duct portion; and    -   a transition portion extending between the first and second duct        portions, wherein the transition portion has a length extending        along a side of the first duct portion and a depth extending        away from the side of the first duct portion, wherein the length        is greater than a diameter of the second duct portion.    -   25. The duct intersection according to claim 24, wherein the        length is twice the depth.    -   26. The duct intersection according to claim 24, wherein the        transition portion is flared.    -   27. The duct intersection according to claim 24, wherein the        first duct portion includes an enlarged annular region and the        transition portion extends between the enlarged annular region        and the second duct portion.    -   28. The duct intersection according to claim 24, wherein the        second duct portion extends laterally from the side of the first        duct portion at an angle of less than 90 degrees.    -   29. The duct intersection according to claim 24, wherein the        second duct portion tees into the first duct portion.    -   30. The duct intersection according to claim 24, further        comprising at least one flow modifier having a convex surface        disposed inside one of the first and second duct portions.    -   31. The duct intersection according to claim 30, further        comprising at least one turning vane.    -   32. A method of improving gas flow in an exhaust system        including at least one duct intersection, the method comprising:    -   determining a location of a poor flow zone within the duct        intersection; and    -   injecting a fluid into the duct intersection at the determined        location.

I/we claim:
 1. A duct intersection, comprising: a first duct portion; asecond duct portion extending laterally from a side of the first ductportion; and at least one flow modifier disposed inside one of the firstand second duct portions.
 2. The duct intersection according to claim 1,wherein the flow modifier is a contoured duct liner.
 3. The ductintersection according to claim 2, wherein the contoured duct linercomprises a first contoured wall mated to an inside surface of the ductand a second contoured wall mated to the first contoured wall.
 4. Theduct intersection according to claim 3, wherein the second contouredwall comprises a refractory material.
 5. The duct intersection accordingto claim 2, wherein the second duct portion tees into the first ductportion.
 6. The duct intersection according to claim 5, wherein thecontoured duct liner is mounted inside the first duct portion.
 7. Theduct intersection according to claim 5, wherein the contoured duct lineris mounted inside the second duct portion.
 8. The duct intersectionaccording to claim 1, wherein the flow modifier includes at least oneturning vane.
 9. The duct intersection according to claim 1, wherein theflow modifier comprises molded refractory material.
 10. The ductintersection according to claim 1, wherein the second duct portionextends laterally from the side of the first duct portion at an angle ofless than 90 degrees.
 11. A contoured duct liner for use in a ductintersection, comprising: a first wall contoured to mate with an insidesurface of a duct intersection; and a second wall attached to the firstwall, wherein the second wall is contoured to modify the direction ofgas flow within the duct intersection.
 12. The contoured duct lineraccording to claim 11, wherein the second wall includes at least oneconvex surface.
 13. The contoured duct liner according to claim 11,wherein the second wall comprises a refractory material.
 14. A cokingfacility exhaust system, comprising: an emergency stack; a crossoverduct extending laterally from a side of the emergency stack; and acontoured duct liner, including a convex surface operative to modify thedirection of gas flow proximate an intersection of the emergency stackand crossover duct.
 15. The coking facility exhaust system according toclaim 14, further comprising a second contoured duct liner disposed onan inside surface of the crossover duct.
 16. An improved coking facilityexhaust system including an emergency stack and a crossover ductextending laterally from a side of the emergency stack, the improvementcomprising: a contoured duct liner, including a convex surface operativeto modify the direction of gas flow proximate an intersection of theemergency stack and crossover duct.
 17. A method of improving gas flowin an exhaust system including at least one duct intersection, themethod comprising: determining a location having undesirable flowcharacteristics within the duct intersection; and providing a flowmodifier in the duct intersection at the determined location.
 18. Themethod according to claim 17, wherein the location is determined with acomputer aided design system.
 19. The method according to claim 17,wherein the location is determined by measuring conditions at the ductintersection.
 20. The method according to claim 19, wherein theconditions are selected from the group consisting of temperature,pressure, and velocity.
 21. The method according to claim 17, whereinthe flow modifier is a contoured duct liner.
 22. The method according toclaim 17, wherein the flow modifier is at least one turning vane. 23.The method according to claim 17, further comprising gunning refractorymaterial on an inside surface of the duct intersection at the determinedlocation, thereby providing the convex surface.
 24. A duct intersection,comprising: a first duct portion; a second duct portion extendinglaterally from a side of the first duct portion; and a transitionportion extending between the first and second duct portions, whereinthe transition portion has a length extending along a side of the firstduct portion and a depth extending away from the side of the first ductportion, wherein the length is greater than a diameter of the secondduct portion.
 25. The duct intersection according to claim 24, whereinthe length is twice the depth.
 26. The duct intersection according toclaim 24, wherein the transition portion is flared.
 27. The ductintersection according to claim 24, wherein the first duct portionincludes an enlarged annular region and the transition portion extendsbetween the enlarged annular region and the second duct portion.
 28. Theduct intersection according to claim 24, wherein the second duct portionextends laterally from the side of the first duct portion at an angle ofless than 90 degrees.
 29. The duct intersection according to claim 24,wherein the second duct portion tees into the first duct portion. 30.The duct intersection according to claim 24, further comprising at leastone flow modifier having a convex surface disposed inside one of thefirst and second duct portions.
 31. The duct intersection according toclaim 30, further comprising at least one turning vane.
 32. A method ofimproving gas flow in an exhaust system including at least one ductintersection, the method comprising: determining a location of a poorflow zone within the duct intersection; and injecting a fluid into theduct intersection at the determined location.